1. Field of the Invention
The present invention relates generally to wireless communication systems and, more specifically, to the multiplexing of control information and data information in a physical channel transmitted in the uplink of a communication system.
2. Description of the Art
A communication system includes a DownLink (DL) that conveys transmission of signals from a Base Station (BS or Node B) to User Equipment (UEs) and an UpLink (UL) that conveys transmission of signals from UEs to a Node B. A UE, also commonly referred to as a terminal or a mobile station, may be fixed or mobile and may be a wireless device, cellular phone, personal computer device, and the like. A Node B is generally a fixed station and may also be referred to as a Base Transceiver System (BTS), an access point, or the like.
The UL supports the transmission of data signals carrying information content, control signals providing information associated with the transmission of data signals in the DL, and Reference Signals (RSs), which are commonly referred to as pilot signals. The DL also supports the transmission of data signals, control signals, and RSs.
DL data signals are conveyed through a Physical Downlink Shared CHannel (PDSCH). UL data signals are conveyed through a Physical Uplink Shared CHannel (PUSCH).
DL control signals may be broadcast or sent in a UE-specific nature. Accordingly, UE-specific control signals can be used, among other purposes, to provide UEs with Scheduling Assignments (SAs) for PDSCH reception (DL SAs) or PUSCH transmission (UL SAs). The SAs are transmitted from Node B to respective UEs using Downlink Control Information (DCI) formats through respective Physical Downlink Control CHannels (PDCCHs).
In the absence of a PUSCH transmission, a UE conveys Uplink Control Information (UCI) through a Physical Uplink Control CHannel (PUCCH). However, when it has a PUSCH transmission, the UE may convey UCI together with data information through the PUSCH.
The UCI includes ACKnowledgment (ACK) information associated with the use of a Hybrid Automatic Repeat reQuest (HARQ) process. The HARQ-ACK information is sent in response to the reception of Transport Blocks (TBs) by the UE conveyed by the PDSCH.
The UCI may also include a Channel Quality Indicator (CQI), or a Precoding Matrix Indicator (PMI), or a Rank Indicator (RI), which may be jointly referred to as Channel State Information (CSI). The CQI provides Node B with a measure of the Signal to Interference and Noise Ratio (SINR) the UE experiences over sub-bands or over the whole operating DL BandWidth (BW). This measure is typically in the form of the highest Modulation and Coding Scheme (MCS) for which a predetermined BLock Error Rate (BLER) can be achieved for the transmission of TBs. The MCS represents the product of the modulation order (number of data bits per modulation symbol) and of the coding rate applied to the transmission of data information. The PMI/RI informs Node B how to combine the signal transmission to the UE from multiple Node B antennas using the Multiple-Input Multiple-Output (MIMO) principle.
FIG. 1 illustrates a conventional PUSCH transmission structure. For simplicity, the Transmission Time Interval (TTI) is one sub-frame 110 which includes two slots. Each slot 120 includes NsymbUL symbols used for the transmission of data signals, UCI signals, or RSs. Each symbol 130 includes a Cyclic Prefix (CP) to mitigate interference due to channel propagation effects. The PUSCH transmission in one slot may be either at a same or different BW as the PUSCH transmission in the other slot. Some symbols in each slot are used to transmit RS 140, which enables channel estimation and coherent demodulation of the received data and/or UCI signals. The transmission BW includes frequency resource units that will be referred to herein as Physical Resource Blocks (PRBs). Each PRB includes NscRB, sub-carriers, or Resource Elements (REs), and a UE is allocated MPUSCH PRBs 150 for a total of MscPUSCH=MPUSCH·NscRB REs for the PUSCH transmission BW. The last sub-frame symbol may be used for the transmission of Sounding RS (SRS) 160 from one or more UEs. The SRS provides Node B with a CQI estimate for the UL channel medium for the respective UE. The SRS transmission parameters are semi-statically configured by Node B to each UE through higher layer signaling such as, for example, Radio Resource Control (RRC) signaling. The number of sub-frame symbols available for data transmission is NsymbPUSCH=2·(NsymbUL−1)−NSRS, where NSRS=1 if the last sub-frame symbol is used for SRS transmission having overlapping BW with PUSCH BW, and NSRS=0 otherwise.
FIG. 2 illustrates a conventional transmitter for transmitting data, CSI, and HARQ-ACK signals in a PUSCH. Coded CSI bits 205 and coded data bits 210 are multiplexed 220. HARQ-ACK bits are then inserted by puncturing data bits and/or CSI bits 230. The Discrete Fourier Transform (DFT) is then performed by the DFT unit 240, the REs are then selected by the sub-carrier mapping unit 250 corresponding to the PUSCH transmission BW from controller 255, the Inverse Fast Fourier Transform (IFFT) is performed by an IFFT unit 260 and finally CP insertion is performed by a CP insertion unit 270, and time windowing is performed by filter 280, thereby generating a transmitted signal 290. The PUSCH transmission is assumed to be over clusters of contiguous REs in accordance to the DFT Spread Orthogonal Frequency Division Multiple Access (DFT-S-OFDMA) method for signal transmission over one cluster 295A (also known as Single-Carrier Frequency Division Multiple Access (SC-FDMA)), or over multiple non-contiguous clusters 295B.
FIG. 3 illustrates a conventional receiver for receiving a transmission signal as illustrated in FIG. 2. After an antenna receives the Radio-Frequency (RF) analog signal and after further processing units (such as filters, amplifiers, frequency down-converters, and analog-to-digital converters) which are not illustrated for brevity, the received digital signal 310 is filtered by filter 320 and the CP is removed by CP removal unit 330. Subsequently, the receiver unit applies a Fast Fourier Transform (FFT) by an FFT unit 340, selects the REs used by the transmitter using a sub-carrier demapping unit 350 under a control of controller 355, applies an Inverse DFT (IDFT) using an IDFT unit 360, an extraction unit 370 extracts the HARQ-ACK bits, and a de-multiplexing unit 380 de-multiplexes the data bits 390 and CSI bits 395.
For HARQ-ACK or RI transmission in a PUSCH, a UE determines the respective number of coded symbols Q′ as shown in Equation (1):
                              Q          ′                =                  min          (                                    ⌈                                                O                  ·                                      β                    offset                    PUSCH                                                                                        Q                    m                                    ·                  R                                            ⌉                        ,                          4              ·                              M                sc                PUSCH                                              )                                    (        1        )            
where O is a number of HARQ-ACK information bits or RI information bits, βoffsetPUSCH is informed to the UE through RRC signaling, Qm is a number of data bits per modulation symbol (Qm=2, 4, 6 for QPSK, QAM16, QAM64, respectively), R a data code rate for an initial PUSCH transmission for the same TB, MscPUSCH is a PUSCH transmission BW in a current sub-frame, and ┌ ┐ indicates a ceiling operation that rounds a number to its next integer. The maximum number of HARQ-ACK or RI REs is limited to the REs of 4 DFT-S-OFDM symbols (4·MscPUSCH).
The number of HARQ-ACK or RI coded symbols in Equation (1) is derived subject to achieving the respective reception reliability target (BLER) depending on the data reception reliability target (BLER). For given UL channel conditions, the data BLER depends on the data MCS, as defined by the product Qm·R, and the link between the HARQ-ACK BLER or RI BLER and the data BLER is established by the βoffsetPUSCH parameter. For a fixed UCI BLER target, the βoffsetPUSCH parameter allows Node B scheduler to vary the data BLER by also varying the βoffsetPUSCH value. For example, from Equation (1), Node B scheduler can increase the data BLER target (by increasing Qm·R) and maintain the same UCI BLER target by applying a same increase to the βoffsetPUSCH value.
The reason for dimensioning the number of coded HARQ-ACK or RI symbols in Equation (1) relative to the initial PUSCH transmission for the same TB is because the respective target BLER is determined relative to the data BLER for the initial PUSCH transmission of the same TB. Moreover, HARQ retransmissions of the same TB may be non-adaptive.
The data code rate R for the initial PUSCH transmission of the same TB is defined as in Equation (2):
                    R        =                              (                                          ∑                                  r                  =                  0                                                  C                  -                  1                                            ⁢                              K                r                                      )                    /                      (                                          Q                m                            ·                              M                sc                                  PUSCH                  -                  initial                                            ·                              N                symb                                  PUSCH                  -                  initial                                                      )                                              (        2        )            
where C is a total number of data code blocks of the TB, Kr is a number of bits for data code block number r, and MscPUSCH-initial and NsymbPUSCH-initial are respectively a PUSCH BW (number of sub-carriers) and a number of DFT-S-OFDM symbols. Therefore, Equation (1) is equivalent to Equation (3):
                              Q          ′                =                  min          (                                    ⌈                                                                    O                    ·                                          β                      offset                      PUSCH                                        ·                                          M                      sc                                              PUSCH                        -                        initial                                                                              ⁣                                      ·                                          N                      symb                                              PUSCH                        -                        initial                                                                                                                                  ∑                                          r                      =                      0                                                              C                      -                      1                                                        ⁢                                      K                    r                                                              ⌉                        ,                          4              ·                              M                sc                PUSCH                                              )                                    (        3        )            
When the UE receives one TB, the HARQ-ACK includes 1 bit which is encoded as a binary ‘1’ if the TB is correctly received (positive acknowledgement or ACK), or as a binary ‘0’ if the TB is incorrectly received (negative acknowledgment or NACK). When the UE receives two TBs, the HARQ-ACK includes 2 bits [o0ACK o1ACK] with o0ACK for TB 0 and o1ACK for TB 1. The encoding for the HARQ-ACK bits is given in Table 1 below, where o2ACK=(o0ACK+o1ACK) mod 2 to provide a (3, 2) simplex code for the 2-bit HARQ-ACK transmission.
TABLE 1Encoding for 1-bit and 2-bits of HARQ-ACKmEncoded HARQ-ACK - 1 bitEncoded HARQ-ACK - 2 bits[o0ACK y][o0ACK o1ACK o2ACK o0ACK o1ACK o2ACK][o0ACK y x x][o0ACK o1ACK x x o2ACK o0ACK x x o1ACK o2ACK x x][o0ACK y x x x x ][o0ACK o1ACK x x x x o2ACK o0ACK x x x x o1ACK o2ACKx x x x
For CQI/PMI multiplexing in a PUSCH, a UE determines a respective number of coded symbols Q′ as shown in Equation (4):
                              Q          ′                =                  min          (                                    ⌈                                                                    (                                          O                      +                      L                                        )                                    ·                                      β                    offset                    PUSCH                                                                                        Q                    m                                    ·                  R                                            ⌉                        ,                                                            M                  sc                  PUSCH                                ·                                  N                  symb                  PUSCH                                            -                                                Q                  RI                                                  Q                  m                                                              )                                    (        4        )            
or Equation (5):
                              Q          ′                =                  min          (                                    ⌈                                                                                          (                                              O                        +                        L                                            )                                        ·                                          β                      offset                      PUSCH                                        ·                                          M                      sc                                              PUSCH                        -                        initial                                                                              ⁣                                      ·                                          N                      symb                                              PUSCH                        -                        initial                                                                                                                                  ∑                                          r                      =                      0                                                              C                      -                      1                                                        ⁢                                      K                    r                                                              ⌉                        ,                                                            M                  sc                  PUSCH                                ·                                  N                  symb                  PUSCH                                            -                                                Q                  RI                                                  Q                  m                                                              )                                    (        5        )            
where O is a number of CQI/PMI information bits and L is a number of Cyclic Redundancy Check (CRC) bits given by
  L  =      {                                        0                                              O              ≤              11                                                            8                                otherwise                              ,      and QCQI=Qm·Q′. If RI is not transmitted, then QRI=0. For CQI/PMI channel coding, convolutional coding is used if O>11 bits and (32, O) Reed-Mueller (RM) block coding is used if O≤11 bits. The code words of the (32, O) block code are a linear combination of the 11 basis sequences denoted by Mi,n. Denoting the input sequence by o0, o1, o2, . . . , oO-1 and the encoded CQI/PMI block by b0, b1, b2, b3, . . . , bB-1 B=32, it is
            b      i        =                  ∑                  n          =          0                          O          -          1                    ⁢                        (                                    o              n                        ·                          M                              i                ,                n                                              )                ⁢        mod        ⁢                                                  ⁢                                                ⁢        2              ,i=0, 1, 2, . . . , B−1. The output sequence q0, q1, q2, q3, . . . , qQCQI-1, is obtained by circular repetition of the encoded CQI/PMI block as qi=b(i mod B), i=0, 1, 2, . . . , QCQI−1.
Among the UCI, HARQ-ACK has the highest reliability requirements and the respective REs are located next to the RS in each slot in order to obtain the most accurate channel estimate for their demodulation. When there is no CQI/PMI transmission, RI is placed at the symbols after the HARQ-ACK, while CQI/PMI transmission is uniformly multiplexed throughout the sub-frame.
FIG. 4 illustrates UCI multiplexing in a PUSCH sub-frame. The HARQ-ACK bits 410 are placed next to the RS 420 in each slot of the PUSCH sub-frame. The CQI/PMI 430 is multiplexed across all DFT-S-OFDM symbols and the remaining bits of the sub-frame carries transmission of data bits 440. As the multiplexing is prior to the DFT, a virtual frequency dimension is used for the UCI placement.
MIMO techniques are associated with signal transmissions from multiple antennas in at least partially (if not fully) overlapping time-frequency resources. The rank S of a MIMO transmission is defined as the number of spatial layers and is always smaller than or equal to the number of UE transmitter antennas T. In the UL, when the transmitter antennas are from the same UE, the MIMO technique is referred to as Single-User MIMO (SU-MIMO). When the transmitter antennas are from different UEs, the MIMO technique is referred to as Multi-User MIMO (MU-MIMO). UL SU-MIMO is typically associated with T=2 or T=4.
Different SU-MIMO techniques can be used to target different operating environments. For example, precoding with rank-1 can be used to improve coverage while spatial multiplexing with rank-4 can be used to improve Spectral Efficiency (SE) and increase data rates. The precoder is a S×T matrix. Multiple spatial streams can be encoded either jointly in a single Code Word (CW) or separately in multiple (typically two) CWs. The tradeoff of using multiple CWs is that the MCS for the respective multiple sets of spatial streams can be individually adjusted and Serial Interference Cancellation (SIC) receivers can be used which can improve SE over Minimum Mean Square Error (MMSE) receivers at the expense of increased feedback overhead over using a single CW.
FIG. 5 illustrates a CW-to-layer mapping. At most 2 CWs exist and each CW is associated with a TB (one TB can be segmented into multiple code blocks C). Each TB is associated with one HARQ process and one MCS. For rank-1 transmission 510, a single CW, CW0, corresponding to a single spatial layer is precoded, either for 2 (1×2 precoder) or for 4 (1×4 precoder) UE transmitter antennas. For rank-2 transmission 520, two CWs, CW0 and CW1, corresponding to two spatial layers are precoded, either for 2 (2×2 precoder matrix) or for 4 (2×4 precoder matrix) UE transmitter antennas. For rank-3 transmission 530 (applicable only for 4 UE transmitter antennas), two CWs, CW0 and CW1, corresponding to three spatial layers are precoded (3×4 precoder matrix) where CW0 is transmitted using one spatial layer and CW1 is transmitted using two spatial layers. For rank-4 transmission 540 (applicable only for 4 UE transmitter antennas), two CWs, CW0 and CW1, corresponding to four spatial layers are precoded (4×4 precoder matrix) where each CW is transmitted using two spatial layers.
For UCI multiplexing in a PUSCH with SU-MIMO transmission, the only practical choices are to either multiplex UCI in one CW or in both CWs. The present invention considers the case that both CWs are used. The UCI is equally replicated across all spatial layers of both CWs and Time Division Multiplexing (TDM) between UCI and data is such that the UCI symbols are time-aligned across all layers.
FIG. 6 illustrates the above principle for the case of HARQ-ACK and 2 layers (corresponding to 2 CWs). The same REs and DFT-S-OFDM symbols are used for multiplexing HARQ-ACK 610 in the first spatial layer (Layer 0 620) and for multiplexing HARQ-ACK 630 in the second spatial layer (Layer 1 640).
When UCI is multiplexed into multiple spatial layers and multiple CWs (multiple TBs) of the same PUSCH transmission with SU-MIMO, the previous expressions for determining the number of REs used for UCI transmission are no longer applicable. Moreover, Node B scheduler may assign different BLER operating points to the different TBs conveyed respectively by the different CWs (for example, in order to improve the performance of a SIC receiver, the initial reception of CW0 may be more reliable than of CW1).
Therefore, there is a need to determine the number of coded UCI symbols in each spatial layer in a PUSCH with SU-MIMO transmission.
There is another need to allow reliable reception of UCI transmitted in multiple TBs when these TBs have different reception reliability characteristics.
There is another need to simplify the processing for the reception of UCI transmitted in multiple TBs.
Finally, there is another need to determine the number of coded UCI symbols in each spatial layer in a PUSCH with transmission of a single TB corresponding to a retransmission of a HARQ process having multiple TBs in the initial PUSCH transmission that include the single TB.